Wednesday, January 31, 2007

Apparently one of the many things with Alfred P. Sloan's name (and some of his money) on it is the annual Alfred P. Sloan Prize at the Sundance Film Festival. The prize of $20,000 goes to a filmmaker whose film either focusses on science or technology, or has a scientist or mathematician as a main character. This year's winning film is "Dark Matter," a film by Chen Shi-Zheng based on the University of Iowa murders in 1991. Science? Murder? The general lore behind this sad story is that graduate Gang Lu was rather displeased that he was not awarded some prestigous prize for his dissertation work. In the movie setting, apparently they are all cosmologists instead of mere physicists. The fantastic aspect of this seemingly minor change is that one of the characters does the infamous "Dark Matter Rap" written by Ohio State's very own David Weinberg (lyrics here, and! mp3 here). Unfortunately, the rapper is one of the ones who is murdered ... but I still can't wait to see the film. And with Meryl Streep as one of the "stars," how much better can it get??

Monday, January 29, 2007

The LBT was recently featured on the Discovery Channel's show "Really Big Things." The LBT, or Large Binocular Telescope, is a, well, really big telescope Ohio State is helping build on Mount Graham in Arizona. It's got two 8.4-m (that's 9.1 yards) diameter primary mirrors—for perspective, in the picture below, the mirrors are the two round shiny things.But this post isn't actually about the LBT at all. It's about the Discovery Channel's depiction of science while attempting to be "funny."

What really angers me about this episode is the attitude of the show's host/interviewer "Matt," and thus the editors, etc. of the entire show. Whenever the conversation would drift towards science—you know, the reason this telescope is being built—the host would start trying to crack jokes about how confusing it is and how he doesn't understand it. Yes, the LBT is an amazing feat of engineering, and, yes, it's really big, and yes, we (as astronomers) will be able to do mind-boggling awesome things with it. But that doesn't mean that the driving science behind building it can't be explained—in fact, I think the scientists and engineers they interviewed did a fantastic job of explaining why astronomers want large mirrors and high resolution ("like an HDTV").

What gets me is how the host was obviously pretending to be stupid/ignorant and then trying to make a joke out of it. For example, at some point he asks if the telescope will be able to be used to look "back in time"—obviously he knows the answer is yes, and I highly doubt that someone would be able to even get a job hosting a show like this without having some proclitivity towards scientific thinking. The fact that looking far out in space is like looking back in time because it takes a long time for the light from far away to reach us is a standard explanation for astronomers, and I think the astronomer doing the explaining explained it well given the time constraints. And then the host was like, whoa, I'm in a time machine, that's too much for me.

Seriously? I applaud the Discovery Channel for trying to reach a different demographic (i.e., not "nerds"), but are they now implicitly supporting the idea that "science is hard" and "normal people will never be able to understand science"? Let's get this straight once and for all: science is nothing to be afraid of. Sure, there are levels of understanding which the average person won't be able to reach after a brief explanation—there are reasons why people spend so many years in school studying this stuff, after all—but that doesn't mean there isn't some level at which they should be able to understand how their computer works or why we know the universe was once a hot, dense, goupy soup of fundamental particles. This is part of what it means to be an educated individual in today's society—or at least what it should mean. I'm not saying that everyone should already have such&such knowledge and understanding, but rather, have the willingness to learn more instead of being afraid of the everso slightly mathematical unknown.

At least the Discovery Channel has the "hey, this is really cool" aspect figured out... but I am disappointed that they are also playing around in the "let's make ignorance and stupidity look funny" field.

Tuesday, January 23, 2007

Many of you have told me that you like it when I give "my perspective." I'm not sure what that means, but here's a bit of my perspective for you: life sucks when it's cold outside.

Now, the cold and the suckage are probably not actually causally related, but I can at least assume they are. Winter: cold and busy and stressful. Summer: warm and busy and not stressful. Clearly, I can blame the temperature. Well, that, and in a Perfect World, I wouldn't waste two minutes putting on complicated clothing just because I want/need to *gasp* go outside. Not to mention the gas bills. Oh, yes, and "cold" is another word for "sick," and "sick" is another way of saying, "I'm not really going to get any work done today, but I'm not going to have any fun either."

This quarter I am taking two classes (because there are two classes to take). They are Radiative Gas Dynamics and Observational Cosmology. Observational Cosmology really means, AGN and maybe some observational cosmology if there's time left at the end of the quarter. I'm going to learn a hell of a lot of physics and astronomy this quarter, and it'll be great, but let's examine my schedule for Tuesdays and Thursdays for a moment, shall we. In short, they are Teh Suck. The idea is that we can dedicate the other days of the week to Doing Research, but seriously, days like Tuesdays and Thursdays this quarter make me want to crawl under my covers and get drunk. Specifically, I've got Coffee from 10:30 until Radiative Gas Dynamics starts at 11:10 or so, which goes until 12:30. Then Observational Cosmology launches at 1:30 and goes until 2:48 (:48? what the ... ?). Thursdays are even better because we have colloquium at 3:30 (with unskippable donuts at 3) until 4:30 or so, and speaker harassment at 5. Yick yick yick. I think I also have office hours on Tuesday, at like 4 or something.

Oh, yeah, and I have office hours this quarter. Because I'm apparently TAing and introductory astronomy course. It's not that TAing takes a lot of time—it takes five hours a week, max, and that includes the office hours that will be sparsely attended—it's that it's just something else to keep track of and do. I'm not TAing because my advisor was particularly unwilling to pay me (i.e., to give me an RAship) this quarter, but because I'm supposedly near the end of my current project and they really need TAs this quarter. This is one of the top ten things wrong with the quarter system. The astronomy department has several two-quarter sequence classes; they all either go fall-winter or winter-spring, and so winter just winds up being "let's teach lots and lots of astronomy classes!" time. At least I don't have to go to the class I'm TAing. It's at 9:30AM every single morning. I have the sneaking suspicion that the professor I'm TAing for would really kind of like for me to go to class every day, but is nice (and smart?) enough to not ask me to. Seriously, why do people take this class? I'm sure it's "intersesting," but 9:30AM interesting? If it were something like galaxies or cosmology, I could understand. But this is the solar system. And so far, it's not even "cool" solar system; it's like, zomg what causes a lunar eclipse?! See, this is why I wasn't an astronomy major.*

And, oh yes, I'm apparently close to the end of my current project. Which is to say, I'm finished with my current project, except that I need to actually write the paper. And, apparently, it has been decided that I should have said paper done by February 1. February 1 is terrifyingly soon, in case you hadn't noticed. And, of course, now that I've mentioned it on my blog, I have to have said paper finished by February 1. Well. We'll see how that goes ...

* Please ignore the fact that MIT neither has an astronomy department nor offers a B.S. in astronomy.

Saturday, January 20, 2007

One of my Favorite People in the Whole World (tm) has decided to start a blog. And, so, I must tell you people about it. It is called Spheroid. Its author, Amali, is an undergrad in Physics at MIT and is just totally awesome. She is, in fact, TRULY FASCINATING; she also doesn't like marmalade. If her blog is going to be anything like she is (which I'm guessing it will be) and if her blog is going to be anything like it has been so far (which it has been, so far) then it will be of the abso-friggin-lutely laugh-til-you-cry hilarious—yet subtlely funny—variety. And she loves physics. Amali bounces about physics, in a way most of us only do on the inside, or *gasp* have you forgotten what that kind of excitement feels like?? So far she's already discussed both chocolateandtelescopes—you just can't get better than that.

Mmm, yes, so: if you would like to bring entertainment and the excitement of physics and learning back to your life, add Spheroid to your blogroll—and stop over and say hello!

Friday, January 19, 2007

It was cold and snowy this morning, and now it's just cold. Days like today need memories like this one: we were so grateful it was a cloudy day so that it wasn't too hot. That's my dad's leg over there on the left of the picture. This is near China Beach in Vietnam (we were staying in Hoi An at the time, if I remember correctly); we had rented a motorcycle and ridden out for a nice day at the beach. Saigon beer (cold, with ice!) and a nice Coca-cola ... in the shade, listening to the waves, with the sand in your toes ...

Thursday, January 18, 2007

Many others have already pitched in their comments about this year's Mystery Hunt (including AaronandNoah from my own team). (My earlier post on, "this is what the Mystery Hunt is" can be found here.) The big list-o-puzzles can be found here, and a general description of how the Hunt worked is over here. They do a good job explaining the plot and how the Hunt was structured, so I'm not going to repeat it here.

The team I was on, Metaphysical Plant, consisted of about 35 people at MIT and about 15 in Berkeley doing "remote solving," also known as, "we don't know what to work on, so we'll solve a meta." Having a room dedicated to a Skype connection with Berkeley was also fun, and I think it worked well.

There were very few puzzles this year that I was excited about once while solving them. (Though I wasn't working on it and I'm pretty sure we backsolved it anyhow, I was still highly amused when the Blather puzzle started throwing monkey poo all over the room. My code will start doing this now.)

The puzzles!, in no particular order, except the ones I liked probably come first:

Nur einzelne Zahlen erlaubt!: I enjoyed this puzzle because it was simple and clean, and the solver gets to play with sudokus without "doing a sudoku." I was also really excited once I realized that the phrases that came out were real Japanese words and not just gobbly goop, and I like how they fit into the title. Oh, and for once I got to help a group become un-stuck on something!

Ducks Playing Poker: I can't not mention the "duck konundrum." I mentioned before that puzzles rarely come with "instructions." The duck konundrum is an infamous reversal of this rule. You want instructions? We got instructions. Our team has had a bit of practice with this particular version of puzzle (this is D4), so when we were told to encourage our duck to move one space to the left, we had to call HQ and ask how encourageable our duck was. You never know. I was very happy that this konundrum had no bugs in it (unlike previous ones we've been forced to debug), but the answer was somewhat anticlimatic. I definitely prefered the way D2 worked; it involved trying to find a certain footnote in the author's thesis, which was way cool.

Course Load: This puzzle was also a lot of fun, though much of it may have had to do that with the fact that it came late in hunt and we had a large group working on it after the small group gave up. We wrote the triplets of course numbers on the board and started trying to figure out what to do with them. We tried figuring out how many units each one was worth (a few were "units arranged"), we tried averaging them (they didn't all sum to something divisible by 3), we tried various kinds of "take the nth letter..." and none of these worked. We finally asked Berkeley for a random suggestion; how about adding them? You'd think that averaging them would lead to adding them first, but no, no no. It was very exciting once it started actually working. The actual fake course titles were also kind of amusing.

Negative Ad Campaign: Speaking of funny, this one was really funny. I didn't actually work on it (it came in the middle of Friday night when I was already a sleepy puddle of sleepiness), but the slogans are all hilarious, and it was still being discussed the following day. For example, what's the opposite of Subway's slogan "Eat Fresh"? Vomit Rancid! Hehehe.

The Meta-meta Dodecahedron: Very cool. This was a lot of fun to work on, especially in a big group. We eventually started just trying random-things-you-can-do-to-words-to-get-other-words, and it worked! My only complaint (which a lot of others have had) is that there was no way to solve it without one of the metas. Such as the Round VIII meta, as a random example.

The Round VIII Meta: Alright, so only like everyone has commented on this already. Yes, it was broken or underclued or whatever, and yes, it did hold up the hunt, and yes, if it had been easier the hunt would have ended earlier and perhaps differently. Blahblahblah. My main complaint is that it was basically all we were working on the last few hours of Hunt, and so we were all in a rather annoyed mood at the end. It had quit being fun. (We were still having fun, and Berkeley had busted out the alcohol and the Wii, and we weren't dying to win, so it was all good, but still.)

Manipulating the Masses: Okay, let's talk about giving useless annoying information. Why would you arrange icons like that if the arrangement wasn't important? And providing 9 icons that are ... completely irrelevant? And the random anagrams? Who's ever going to think of anagraming random phrases into names?? We spent a lot of time on this puzzle, but we eventually realized it wasn't going to happen. Luckily, the meta for this round allowed for backsolving,* so when someone asked the room which puzzle we were least likely to actually solve, we all agreed it was this one, so the backsolved answer was called in for this puzzle. It was correct; we were glad.

Overall, I liked that we knew fairly early in the game what the overall structure of the hunt was going to be: this many rounds, with this many puzzles per round, and so on. The early runaround and everyone-finds-the-coin thing was kind of lame. We wanted to do a similar thing last year, but decided not to because, well, there just isn't any way to do it without it being lame. I didn't even know there was a runaround until I noticed we had solved it. Not revealing the structure of the Hunt until after kickoff meant that kickoff was a bit lame as well, but it did mean that it was fun trying to figure out what the real theme was going to be. The events were mostly either kind of lame or totally evil. The Lust event was more on the lame side, but it was short and amusing, and since it was at midnight, lameness was perfectly OK. The Gluttony event was just pure evil, but oh, so amusing. In general, though, it is just plain difficult to write a good non-lame event puzzle. (Sorry; I don't think descriptions for the event puzzles are up yet.)

All in all, though, I had a really fun time. I'm usually better at criticizing than praising; no puzzles had substantial bugs in them, which is certainly something that couldn't be said for some previous Hunts. I'm really glad I Hunted with Metaphysical Plant—it's always good to stay up all night with old friends, and I'm all ready for next year.

Well, that, and you know the scene from A Beautiful Mind when John Nash (Russell Crowe's character) is standing in his office with newspapers and magazines taped up everywhere and all these patterns are jumping out at him? That's my life this week, that, right there. Everything is a puzzle.

* Backsolving a puzzle means that you have solved a meta puzzle and know what format the answers for that round must be in. In this case, the answers were constrained to the extent that we knew exactly which answers they were, just not which puzzles they belonged to.

Wednesday, January 17, 2007

I have a friend living in Cambridge who has recently gotten into Bismuth crystal making. Unlike lead, bismuth is a surprisingly non-toxic (real) heavy element—in fact, it's the reason for the "Bism" in Pepto-Bismol. You can buy it for about $20 a pound. It melts at about 520°F, which is cool enough that you can melt it on the stove. To form a crystal, melt some bismuth on the stove (my friend uses some stainless steel bowls he's dedicated to the mission), and let the molten bismuth sit for a bit. It will begin to cool and crystalize on the surfaces (top and along the sides of the bowl); as it crystalizes, you can kind of break off pieces. It's easier to get lots of small pieces than big ones, and it takes some magic to figure out how to control the color of it—the color is due to a thin layer of bismuth oxide which forms on the surface of the crystal as it cools. If I remember correctly, gold (clearly the least interesting color when up against purple and blue) is due to too much oxidation. It is also possible to make "Bismuth eggs" (or really, "Bismuth any-kind-of-mold-you-might-have") by melting the Bismuth in a mold and then pouring out the molton Bismuth before it gets too crystalized and fills up the mold.

It's difficult to tell from this perspective, but the upper-right one looks like a conical square spiral, both inside and out. The bottom right one (zoomed in below) totally looks like a Frank Gehry building, but that might be because I've seen more of Building 32 in the last weekend than I have in the last year. The two on the left were originally one piece, which was going to be a Christmas tree ornament, but it broke while spending the day in my pocket. I guess I could still glue the two pieces together (they both have relatively flat sides) and stick a piece of string in the glue as well and still end up with a nice ornament.

UPDATE (09/13/2007): My friend has a few corrections and comments to add.

The colors: it's interference coloring, like you get on soap bubbles and oil slicks, based on how thick the oxide grows. As the layer grows in thickness, it will cycle through the colors repeatedly until the oxide gets too thick to easily transmit light, or something, and then I think it just turns gray. With the crystals, the oxide stops growing as the crystal cools. I do think I got more interesting colors when the crystals were cooler before they were exposed to air, so that they oxidized less, but I think it's a mischaracterization to say that one color or another is the result of too much oxidation.

Friday, January 12, 2007

I'm in Cambridge, MA (MIT's campus, to be more specific) this weekend for the annual MIT Mystery Hunt. When it's over, I'm going to want to be able to give a straightforward ohmygodthatwasamazing or awhellthatsucked kind of post, so I figure I should explain now just what Mystery Hunt is and why it's cool enough to be worth taking a 6 day weekend off for.

Mystery Hunt is a weekend long puzzle competition. It kicks off Friday at noon and goes until it's over. Sometimes (like last year) this means roughly midnight Saturday night, whereas other year's it's meant more like 8a.m. Monday morning. The puzzles aren't like "conventional" puzzles: they aren't jigsaw puzzles or crossword puzzles or sudoku puzzles—unless they've been severely ... improved. These are self-contained puzzles. It is rare for a puzzle to come with a set of instructions; I'm sure there will be one exception to this rule this year, and I'm sure it will be a diabolical puzzle. A puzzle might be a set of pictures, a list of words, a list of numbers, an odd looking diagram, a set of mp3 files, or some combination of these. And the puzzle solvers are expected to just come up with the answer.

The other fun thing about Hunt is that it comes with a storyline, some sort of funny plot. If there's any place where regular expressions can save the day, then this is it. The reason it is called a hunt is because all of the teams are nominally hunting for a coin hidden somewhere on campus. Find the coin, win the Hunt. Win the hunt, get to write the Hunt for the next year! Two years ago the team I was on (finally) won, so last year we ran Mystery Hunt. You can see our puzzles, etc. here. Our basic storyline was that there was this evil guy, Professor Moriarty, who had this plot to take over the world (and make a lot of money) by creating a weather-controlling device. He would turn the entire planet into a snowball, except for certain locations of his choosing, such as tropical islands he owned, which he could then charge exorbitant prices for visitors. We (the team running everything) were the good guys, S.P.I.E.S., and we needed to enlist the help of the participating teams in contacting our agents all over the world. Now, each agent had left clues scattered in various cities as to where they were hiding—also known as puzzles. Solving these puzzles would give a list of words, which in turn were some kind of puzzle (known as a "meta" puzzle). The meta answers were passwords which would allow the team to go talk to the agent. (I was Guildenstern. It was fun. I got to toss coins to Rosencrantz and say funny confusing things.) Hidden in the "header" information for each puzzle was another puzzle, which we called antes. Solving the ante would tell the team both which city they needed to "travel" to next, and which agent they should expect to find there. The final meta answer was "Prof Moriarty," signalling that the team was ready for endgame: literally a run around campus following different clues and getting past different obstacles using information learned from past agents. After defeating Moriarty, the team still had to find the "key" (i.e., the coin) to the weather machine—a snowglobe hidden in an airduct in a sub-basement on the far side of campus. Other hunts have had other fun themes: there was the Monopoly hunt, the "Hunt of Horror", the Matrix/Time Bandits hunt, the Smallville hunt, etc. etc. etc. One big thing people always speculate about pre-hunt is what the theme will be. The "Lord of the Rings" theme and the "Figure Out What The Mystery Hunt Theme Is" theme are always too obvious; Pinky and the Brain trying to take over the world would be too annoying (and, besides, Pinky was one of our agents last year). What will it be, what will it be?

Another question I often get about Mystery Hunt is just who does it and just how large it is. Last year, approximately 2000 people on foo number of teams participated. A good hunt is challenging for the teams with really good puzzle solvers, but still fun for that group of four friends who has never tried solving a puzzle before. A good hunt has plenty to do for a team with dozens of members, but is not overwhelming for a team with only ten. The organizers almost always make sure that it is impossible for a team to win—but still possible to have fun!—if the team does not have members with an intimate knowledge of MIT's campus, computer system, classes, etc. It is, after all, technically a student group and completely run from MIT's campus. The team I hunted on my four years at MIT was based in my dorm; we took over the place, with approximately 100 people on our team (though in later years, a good chunk of those were hunting remotely from Berkeley, as they are again this year). Other teams are just a group of friends who like solving puzzles together and are have headquarters in some classroom or lab on campus. The team I am on this year is more like this second kind of team: not all of us wanted to go back to a dorm where we know few people, and would rather have a more exclusive team than brushing elbows with annoying freshmen. And, trust me, after two nights of not-sleeping-really-all-that-much, one develops a much more inclusive sense of just who qualifies as "annoying."

If you want some warm-up fun, you can try solving the puzzle I had in the Hunt last year. Only 3 teams got to it because it was towards the end of the Hunt, but I still really like it—but then, I might be biased. It's called "Numeracy." Here it is, but you'll probably want to look at it in simple plain text. I'll even give you two hints: the answer is a nine letter word, and one of the following numbers has several special qualities you will want to take note of:

Wednesday, January 10, 2007

I don't normally jump on board when big press releases come out with some new "revolutionary" astronomical discovery, and I don't normally give link dumps to what other people have to say, but when it's my former advisor whose name is being plastered all over, I can't help but say a little something. Of course, the big news was released two days ago, so I'm a little late.... Others (see Galactic Interactions and Cosmic Variance, for example) have already given nice lengthy explanations of the results. You can also take a look at the press release and the paper (subscription required). Essentially, gravity bends the path light travels in much the same way it bends the path of a thrown baseball. By looking at the distortions of faraway galaxies due to all of the intervening matter, astronomers can map out the 3-D mass distribution of the universe as shown above. (If you want a slightly more in depth discussion of what "distortions of faraway galaxies" means, you can see my earlier post on weak lensing.) This particular piece of research isn't all that revolutionary: they are using techniques that have been used before and a fairly well-established method, but the amount and quality of the data is somewhat mind-numbing. To get really high resolution data, you have to go to space, which is why the main dataset for this project is from the Hubble Space Telescope (HST). But you also need a huge area of sky for this kind of weak lensing project... and HST doesn't exactly see a lot of the sky at once, which is why this data corresponds to 575 separate pointings of the telescope.

And, oh yes, COSMOS (the multi-observatory project this research stems from) long ago won my prize for largest stretch for an acronym: Cosmic Evolution Survey?!

And since I'm playing the day-late, dollar-short bandwagon game anyhow, yes, please, I would like an iPhone (plus 2 year Cingular plan) as a gift. Thank you.

Monday, January 08, 2007

Apparently Rob Knop over at Galactic Interactions tagged me a bit ago in some sort of blog meme-y thing. So, of course, I have no choice but to comply.

The rules (as copied from Rob as copied from Doug Natelson as presumably copied from someone else and so on):

In this game I’m supposed to grab the nearest book, go to page 123, go to the fifth sentence, and write down the next three sentences. Then I’m to tag three more people, presumably ones that I think will play the game.

I'm sitting right next to my bookshelf, but the nearest book to me is Ernest Hemingway's The Snows of Kilimanjaro and Other Stories, original copyright 1927, this printing is 1970 and cost $1.65. I haven't read most of the stories yet—I've been meaning to, really!—but the book currently claims the very important job of being the object on which my right computer speaker normally sits.

Page 123 is near the beginning of "The Short Happy Life of Francis Macomber." I can't count to three very accurately, so here's the relevant 3±2 sentences:

"Might put it on," said Wilson."You know you have a very red face, Mr. Wilson," she told him and smiled again."Drink," said Wilson."I don't think so," she said. "Francis drinks a great deal, but his face is never red."

Friday, January 05, 2007

This is in regards to NASA cutting funding for the Space Interfermetry Mission (SIM), a mission which would be able to do all sorts of awesome things:

The decision to cut funding has not gone down well, with Gould citing "stupidity" as one reason for the cut.-- Nature, Vol 445, 4 January 2007

The rest of the article, entitled Alien Earth (subscription needed, sorry), is a concise, fairly interesting discussion of the prospects of finding an Earth-like planet around another star, something in which many astronomers have invested a lot of time—and bet money.

Thursday, January 04, 2007

A few weeks ago, some friends asked me whether or not there are a googol particles in the universe. I copped out at the time, pleading hunger, but it's an interesting question, so I found myself trying to answer it yesterday.

First off, a googol is defined as 10100, or a 1 followed by 100 zeros. It's a big number, which is why the Google people wanted to name their company after it; unfortunately one of their first buyers wasn't very good at spelling... I'm also going to define "in the universe" to mean "in the known, observable universe." Obviously, if the actual universe is infinitely large, then there will be more than a googol particles in it. Second is the question of what we mean by "particle." I'll start by assuming that particle means "atom," specifically hydrogen or helium atoms, since there are relatively few other atoms around. I'm also going to take "known universe" to mean "observable universe," and for both of these terms to refer to the entire observable universe at an age of 13.7 billion years old. This isn't actually how the universe is observed; because it takes time for light to travel to us, the farthest away we can see in the universe corresponds to when the universe was very young. Taking this into account would needlessly complicate the question and the calculations.

To get a feel for numbers of particles in big, massive things: how many particles are there in the Sun? The mass of the Sun is roughly 2 x 1057 times that of the mass of the proton, and since about one out of every four atoms in the Sun is a helium atom (which has the same mass as four protons), there are roughly 1057 particles in the Sun.

So how many particles are there in our galaxy, the Milky Way? The mass of the Milky Way is difficult to define, and we have to be careful to only talk about the baryonic mass for now—that is, the mass that is in the atoms we are trying to count. Let's say it is 1011 solar masses; the number of particles in the Milky Way is therefore 1011 x 1057 = 1068.

From here, we can estimate how many particles are in the known universe if we have a good estimate for how many galaxies are in the known universe. This is a tricky number to estimate, because we can't actually see all of these other galaxies. We are also assuming that the Milky Way is a typical galaxy of typical mass. The internet gives a lot of different numbers for the "total number of galaxies in the universe." NASA's "ask an astronomer" page claims 125 billion, which is the same as 1.25 x 1011; other sources give similar answers, so I'll use 1011. Under these assumptions, we calculate that there are on the order of 1079 "particles" (specifically, atoms) in the known universe.

Another way to do this calculation is to first figure out the number density of atoms for the universe, and then multiply by the total volume of the known universe to obtain a total number of atoms. I don't really feel like going into cosmology right now, but essentially, the density of the universe is inexorably linked with its geometry. We know that that universe is pretty damn flat, so we know what the density is fairly well. ("Flat" here means just what it sounds like; you can think of it as meaning that the three angles of a triangle have to add up to 180°.) This "critical" density is approximately 10-29 g/cm3. This is really really tiny: for comparison, the density of water is 1 g/cm3, the density of air at sea level is roughly 10-3 g/cm3, and the density of air in the best vacuum that can be made on earth is 10-20 g/cm3. Cosmologists tell us that only 4% of the universe is made up of atoms, so the density of atoms is more like 4 x 10-31 kg/m3. The mass of a typical atom is still about the mass of two protons, so this corresponds to about 1 x 10-7 atoms per cubic centimeter. (If you don't like fractional atoms, you can think of this as about 1 atom in every ten cubic meters instead.) The volume of the observable universe is determined by its radius. Even though the universe is 13.7 billion years old, its radius is not 13.7 billion lightyears; it's actually more like 93 billion lightyears, or about 9 x 1026 m. This gives us a volume of 3 x 1081 m3, and a total number of atoms in the observable universe of about 1077. I put a lot of assumptions and simplifications into these calculations, so it isn't too surprising that they give slightly different results. When I was doing the calculations yesterday, I was getting more like 1080 for both methods.

So we have determined that there are fewer than a googol atoms in the observable universe. This number won't increase by much if we expand the definition of "particle" to mean all electrons and quarks, the most fundamental particles of matter. But what if we include photons and neutrinos? The ground-up way to do this calculation is to start with a number density of photons (approximately 400 per cubic centimeter) and a number density of neutrinos (approximately 200 per cubic centimeter). Multiplying by the same volume as above, we now get a total of 2 x 1089 particles. There are therefore fewer than a googol known particles in the known universe. An easy check this number—as well as an alternate way of doing the calculation—involves using the known baryon-to-photon ratio of roughly 10-10. ("Baryon" being the word used in cosmology for "stuff that turns into atoms.") This is in fact approximately the ratio between the two total number of atoms and the total number of photons (and neutrinos) we calculated.

I said above that there this means that there are fewer than a googol known particles in the known universe. I have already mentioned that once we no longer restrict ourselves to the observable universe then there can clearly be more particles, but the distinction of known particles is important as well. I said earlier that about 4% of the universe by mass is made up of atomic-like particles; about 20% of the universe is made up of some other kind of mass that we don't really know what is, known as dark matter. A popular assumption is that the dark matter is some kind of as-yet unknown, un-detected particle—with some currently unkown mass. Using the calculation above, if there are going to be a googol dark matter particles in the observable universe, then the dark matter particle would need to be about 10-20 as massive as a proton—that's tiny—so stupidly small that it is in fact ruled out by the fact that we observe the universe to have structure. Such a small mass for the dark matter particle would lead to what is known as the "Hot Dark Matter" scenario; essentially, if the dark matter particle has very little mass, then regular matter won't get cold enough to condense and form nice things like stars and galaxies.

about me and my blog

I'm a graduate student in astronomy in the cloudy midwest. I have a "cozy" little apartment and an office desk by a big window. If I find something interesting to write about, I usually do; if everything is really boring, I write about that as well (unless I don't).